Aggregate checking of a condition on a group of hosts

I want to be alerted when a certain number of servers require a reboot. Ubuntu systems have an easy way to check this and my current setup has a simple check that returns a warning status whenever this condition exists. But instead of an alert for each of them, I’d like to use the aggregate functionality and get a single alert. I read this (Tutorial: Using Check Aggregates in Sensu Go), but I had a couple of questions:

  1. I wasn’t sure that I could prevent the “source checks” from causing alerts themselves.
  2. I didn’t understand the distinction between a Entity Aggregates and Check Aggregates.

Is there a concise explanation of how to do write an on-host check that doesn’t alert, but provides status to a “meta-check” that looks at the results of those checks and does alert?